Plasticity of neuropeptidergic neoplasm cells in the primary and metastatic Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare and highly aggressive cutaneous carcinoma with characteristics of neuroendocrine tumor. We performed immunohistochemical analysis to demonstrate the presence of various neuropeptides within cells of MCC resected from a 75-year old woman. The cells of primary tumor of cheek were compared with the cells of regional right submandibular metastatic tumor which was found eight months later. A double-staining IHC for the pan-neuronal marker, PGP 9.5, and selected neuropeptides in the tissue material obtained from both locations was performed. Single multipolar cells in the main mass of primary tumor stained positively for PGP 9.5 and such neuropeptides as GAL, VIP, PACAP, NPY and CGRP. Moreover, we demonstrated for the first time the presence of neuropeptides in metastatic MCC cells. In the metastatic tumor, cells showing the co-localization of PGP-9.5 and neuropeptides were more numerous, mostly of oval shape, and significantly smaller than in the primary tumor. Thus, the progression of MCC may be associated with the acquisition by its cells of new morphological and biological features.